Large RPM and Vacuum drop when shifting from park to gear

Mattax said
Here's an example of the timing changes with rpm due to the mechanical advance.
Initial timing for for this engine/distributor combo was 0*, plus or minus 2.5*
View attachment 1715602848

You've measured around 15* at 900 and 20* at 1100 rpm.
Lets put that on the same graph paper so you can see why that would be normal advance for many distributors.
View attachment 1715602849

An original Chrysler distributor will have a metal tag on the side.

these graphs are awesome. And yes, I understand what you say about the distributor and how I'm already seeing mechanical advance at my idle speed.

I'll have another look at it tomorrow, but I think my distributor is an OEM style one. If this is the case, could I correct when my mechanical advance comes in with heavier springs? Or will I need a different ditributor?